Automatic multi-level therapy based on morphologic organization of an arrhythmia

ABSTRACT

Methods and systems for selecting tachyarrhythmia therapy based on the morphological organization level of the arrhythmia are described. Morphological organization levels of arrhythmias are associated with cardiac therapies. The morphological organization levels are related to cardiac signal morphologies of the arrhythmias. An arrhythmia episode is detected and the morphological organization level of the arrhythmia episode is determined. A cardiac therapy associated with the morphological organization level of the arrhythmia episode is delivered to treat the arrhythmia. For example, the morphological organization levels may be associated with the cardiac therapies based on one or more of retrospective database analysis, patient therapy tolerance, and physician input. The associations may be static or may be dynamically adjusted based on therapy efficacy.

RELATED PATENT DOCUMENTS

This is a divisional of U.S. patent application Ser. No. 11/209,976,filed on Aug. 23, 2005, now U.S. Pat. No. 7,908,001, to which priorityis claimed under 35 U.S.C. §120, and which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to cardiac therapy devices andmethods, and, more particularly, to automatic selection oftachyarrhythmia therapies based on morphological organization of thetachyarrhythmia.

BACKGROUND OF THE INVENTION

Proper cardiac function relies on the synchronized contractions of theheart at regular intervals. When the heart is functioning normally,synchronized cardiac contractions are initiated at the sinoatrial nodeand the heart is said to be operating in normal sinus rhythm. However,if contractions of the heart become irregular or uncoordinated, or ifthe contraction rate is too fast or too slow, the heart rhythm isdescribed as arrhythmic. Cardiac arrhythmia may be caused, for example,by disease processes or from aberrant electrical conduction patternsoccurring in the heart tissue. Cardiac arrhythmia impairs cardiacpumping efficiency and some types of cardiac arrhythmia can be lifethreatening.

A cardiac arrhythmia that originates in an atrial region of the heart isdenoted a supra-ventricular tachyarrhythmia (SVT). Atrial fibrillationand atrial flutter are examples of SVT. Both conditions arecharacterized by rapid, uncoordinated contractions of the atriaresulting in hemodynamically inefficient pumping action.

Another example of SVT is sinus tachycardia, which is an increased heartrate due to exercise or a quick emotional response. In contrast toatrial fibrillation and atrial flutter, sinus tachycardia ischaracterized by rapid, coordinated contractions of the atria resultingin hemodynamically efficient pumping action, compensating for theincreased strain placed upon the body during exercise or quick emotionalresponses. Whereas atrial fibrillation and atrial flutter are “abnormal”(yet not lethal), sinus tachycardia is “normal” (and also not lethal).

Cardiac arrhythmias originating in a ventricular region of the heart aredenoted ventricular tachyarrhythmias. Ventricular tachycardia (VT) ischaracterized by rapid ventricular contractions and can degenerate intoventricular fibrillation (VF). Ventricular fibrillation producesextremely rapid, non-coordinated contractions of the ventricles.Ventricular fibrillation is fatal unless the heart is returned to sinusrhythm within a few minutes.

Implantable cardiac rhythm management (CRM) devices, includingpacemakers and implantable cardioverter/defibrillators, and have beenused to deliver effective treatment to patients with serious cardiacarrhythmias. Cardiac rhythm management devices may treat cardiacarrhythmias with a variety of tiered therapies. These tiered therapiesrange from delivering low energy pacing pulses timed to assist the heartin maintaining pumping efficiency to providing high-energy shocks totreat and/or terminate fibrillation. To effectively deliver thesetreatments, the CRM device must first identify the type of arrhythmiathat is occurring, after which appropriate therapy may be delivered tothe heart.

SUMMARY OF THE INVENTION

The present invention is directed to methods and systems for selectingtachyarrhythmia therapy based on the morphological organization level ofthe arrhythmia. One embodiment of the invention involves a method fordelivering cardiac therapy. Morphological organization levels ofarrhythmias are associated with cardiac therapies. The morphologicalorganization levels are related to cardiac signal morphologies of thearrhythmias. An arrhythmia episode is detected and the morphologicalorganization level of the arrhythmia episode is determined. A cardiactherapy associated with the morphological organization level of thearrhythmia episode is delivered to treat the arrhythmia. For example,the morphological organization levels may be associated with the cardiactherapies based on one or more of retrospective database analysis,patient therapy tolerance, and physician input.

The cardiac therapy delivered may be a multi-level therapy that includesa number of therapy components, such as one or more anti-tachycardiapacing components and/or one or more shock therapy components. After oneor more therapy component is delivered, the method may include sensingfor redetection of the arrhythmia following delivery of one or more ofthe therapy components. Sensing for redetection may occur more often fora more organized arrhythmia episode and less often for a less organizedarrhythmia episode.

In one implementation, associating the morphological organization levelswith the cardiac therapies involves associating the morphologicalorganization levels with therapy wander times. The therapy wander timesrepresent lengths of time that the cardiac therapies are delivered.

The morphological organization level of the arrhythmia episode may bedetermined based on one or more of morphological regularity of a cardiacelectrogram signal of the arrhythmia episode, entropy of the cardiacelectrogram, and hemodynamic stability of the arrhythmia episode.

According to one aspect of the invention, the morphological organizationlevel of the arrhythmia episode is determined by comparing morphologiesof one or more of the cardiac beat signals of the arrhythmia episode toa template. Alternatively, or additionally, the morphologicalorganization level of the arrhythmia episode may be determined bycomparing a morphology of a cardiac beat signal of the arrhythmiaepisode to a morphology of another cardiac beat signal of the arrhythmiaepisode.

The morphological organization level of the arrhythmia episode may bedetermined based on rate irregularity of the arrhythmia episode, themorphological complexity of a cardiac electrogram signal of thearrhythmia episode, and/or the hemodynamic stability of the arrhythmiaepisode. For example, determining the morphological organization mayinvolve using one or more thresholds respectively associated with one ormore measures of morphological organization.

Associating the morphological organization levels with the cardiactherapies may involve statically or dynamically associating themorphological organization levels with the cardiac therapies. Accordingto one aspect of the invention, the morphological organization levelsmay be associated with the cardiac therapies based on one or more ofhistorical data, patient therapy tolerance and physician input. After aninitial association is made, the associations between the morphologicalorganization levels and the therapies may be dynamically changed basedon efficacy of the cardiac therapies.

Another embodiment of the invention is directed to a cardiac rhythmmanagement device. The cardiac rhythm management device includes aprocessor that is configured to associate the morphological organizationlevels of arrhythmias with cardiac therapies. The processor is alsoconfigured to determine a morphological organization level of anarrhythmia episode based on cardiac signals. An arrhythmia detector isconfigured to detect the arrhythmia episode and therapy circuitrydelivers a cardiac therapy associated with the morphologicalorganization level of the arrhythmia episode. The cardiac rhythmmanagement device typically includes a memory which may be used to storea library of the cardiac therapies and an association map between themorphological organization levels and the cardiac therapies. Accordingto one aspect of the invention, the cardiac rhythm management device ispatient implantable.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method of delivering multi-leveltherapy based on morphological organization of an arrhythmia inaccordance with embodiments of the invention;

FIG. 2 is a diagram illustrating the concept of mapping associationsbetween morphological organization level and arrhythmia therapy inaccordance with embodiments of the invention;

FIG. 3 is a flowchart illustrating a process for dynamic modification ofa multi-level therapy in accordance with embodiments of the invention;

FIG. 4A depicts a method for determining the number of morphologicallysimilar beats in an arrhythmia episode in accordance with embodiments ofthe invention;

FIG. 4B illustrates a process of determining the morphologicalorganization level based on the number of similar beats of an arrhythmiaepisode in accordance with embodiments of the invention;

FIG. 5 is a flowchart illustrating a process of determining themorphological organization level based on the spreadness of the beatfeatures in accordance with embodiments of the invention;

FIG. 6 is a partial view of one embodiment of an implantable medicaldevice that may be used to deliver multi-level therapy based onmorphological organization level of the arrhythmia in accordance withembodiments of the invention; and

FIG. 7 is a block diagram illustrating functional components of animplantable medical device that may be used to deliver multi-leveltherapy based on morphological organization level of the arrhythmia inaccordance with embodiments of the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings forming a part hereof, and inwhich are shown by way of illustration, various embodiments by which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

Ventricular tachyarrhythmias are fast heart rhythms that arise withinone or more ventricles. Atrial tachyarrhythmias, e.g., atrial flutter oratrial fibrillation, are fast heart rhythms that arise within one ormore atria. Electrogram (EGM) or electrocardiogram (ECG) signalsrepresentative of ventricular or atrial tachyarrhythmic beats mayexhibit a number of different morphology patterns. Some types oftachyarrhythmia may exhibit a generally monomorphic pattern. Electrogramsignals representing a monomorphic tachyarrhythmia may have a fairlyregular rhythm and a similar shape or morphology.

Other types of tachyarrhythmia may comprise multi-morphology orpolymorphic tachyarrhythmia. Each beat of a multi-morphology orpolymorphic tachyarrhythmia may be different. Ventricular fibrillationis an example of a polymorphic ventricular tachyarrhythmia that presentsa disorganized, inconsistent morphology.

Episodes of tachyarrhythmia may last only a few beats and may produceminimal symptoms. If the cardiac rate is relatively low, thetachyarrhythmia may be tolerated even if sustained for a number ofminutes. Tachyarrhythmia may be treated using a variety of therapies.For example, in some cases, ventricular tachycardia (VT) may beeffectively treated by pacing at relatively high energy output whencompared to bradycardia pacing. Pacing to mitigate VT may involve one ormore pacing bursts and is typically denoted anti-tachycardia pacing(ATP). Other types of VT may require a more aggressive therapy,including low energy cardioversion shocks and/or high energydefibrillation shocks. Still other types of VT may terminatespontaneously without therapy or may not require therapy.

The most dangerous form of polymorphic ventricular tachyarrhythmia isdenoted ventricular fibrillation, which involves very rapid,small-scale, and uncoordinated contractions. The rapid contractionscause a precipitous drop in blood pressure and compromised hemodynamicoutput. Ventricular fibrillation involving heart rates in excess ofabout 220 beats per minute rarely terminate spontaneously and may befatal without rapid therapeutic intervention.

The present invention is directed to methods and systems forautomatically delivering multi-level arrhythmia therapy selected totreat the particular arrhythmia type based on the morphologicalorganization of the cardiac signals of the arrhythmia episode. Themorphological organization of the arrhythmia may be determined, forexample, by directly evaluating the morphological organization of thecardiac electrical signal, e.g., electrocardiogram (ECG) or electrogram(EGM), or by evaluating variations of features extracted from othercardiac signals, such as hemodynamic sensor signals. The method involvesclassifying ventricular or atrial arrhythmia episodes according tomorphological organization level, and delivering multi-leveltachyarrhythmia therapy associated with the morphological organizationlevel of the arrhythmia episode. In various implementations, arrhythmiasmay be classified based on one or more measures of morphologicalorganization of the electrogram signal, including morphologicalregularity of the cardiac beats (similarity in the morphology of cardiacbeat signals of the arrhythmia), entropy or complexity analysis (measureof the randomness of the electrogram signal of the arrhythmia),hemodynamic status (e.g., as measured by impedance, oxygen saturation,heart sound, activity and/or pressure sensors), and/or by othermeasures. Arrhythmia rate information may also be used in addition toone or more morphological organization measures.

Each arrhythmia morphological organization level is associated with adistinct cardiac therapy scheme (RxS). The cardiac therapy scheme mayinvolve a tiered therapy approach wherein one or more therapy componentsof the therapy scheme provide an increasingly aggressive therapy to thepatient.

FIG. 1 is a flowchart illustrating a method of providing multi-leveltachyarrhythmia therapy in accordance with embodiments of the invention.The method involves associating 110 arrhythmia morphologicalorganization levels with cardiac therapies. The cardiac therapies mayinclude one or more component therapies that are delivered sequentially,for example. The association between cardiac therapies and arrhythmiamorphological organization level may be initially based on analysis ofhistorical data pertaining to the success or failure of various therapyschemes to convert different types of arrhythmia. The mapping ofassociations between therapies and morphological organization level maybe performed automatically by the CRM device or manually by a physicianor other person communicating with the CRM through a programmer, forexample.

If an arrhythmia episode is detected 120, e.g., by examination of rateand/or morphology analysis, the morphological organization level of thearrhythmia is determined 130. The cardiac therapy associated with themorphological organization level is delivered 140.

A general rule of programming different levels of anti-tachycardiatherapy is that the aggressiveness of the therapy is proportional to theseverity of the arrhythmia. Different combinations of ATP and/or shocktherapy components can be programmed for different levels of arrhythmiamorphological organization levels. For example, for a more organizedarrhythmia, a cardiac therapy can be programmed as the followingsequence of therapy components: ATP1→ATP2→APT3→Cardioversion→Shock. Fora more severe, more disorganized arrhythmia, the cardiac therapysequence can be programmed as ATP1→Cardioversion→Shock. For a verysevere, very disorganized arrhythmia, the cardiac therapy sequence canbe programmed as Cardioversion→Shock. Cardioversions and shocks withdifferent energies can be used to make the cardiac therapy complete andpractical. In the above examples, ATP1 and ATP2 may be ATPs withdifferent parameters settings. For example, ATP2 may have more pacingbursts and/or shorter pulse duration and/or higher pacing energy thanATP1.

In some implementations, arrhythmia redetection may be enabled betweentwo components of the cardiac therapy scheme. For example, arrhythmiaredetection may be performed between the ATP1 and ATP2 components and/orthe ATP2 and ATP3 components and/or the ATP3 and Cardioversioncomponents and/or the Cardioversion and Shock components of the firstcardiac therapy sequence example above. In some embodiments, theredetected arrhythmia may be analyzed for determination of themorphological organization of the redetected arrhythmia. The cardiactherapy delivered to treat the initially detected arrhythmia may bemodified so that a cardiac therapy associated with the morphologicalorganizational level of the redetected arrhythmia is delivered to thepatient.

Sequences of therapy components of a programmed cardiac therapy mayinclude more ATP components and more redetection periods for arrhythmiasthat are more organized when compared to the number of ATP componentsand redetection periods for arrhythmias that are less organized. A moreorganized arrhythmia is more likely to be converted by ATP therapy. Evenif one ATP attempt fails to convert the arrhythmia, an additionalattempt or attempts may succeed. Therefore, a cardiac therapy deliveredto treat a more organized arrhythmia may include a number of ATPcomponents. The device may enable redetection periods between two ormore of the ATP components to check if the therapy has converted thearrhythmia. If the arrhythmia has been converted, the device does notdeliver additional components of the programmed therapy.

In contrast, ATP is less likely to be effective if an arrhythmia is orbecomes less organized. Therefore, fewer ATP components are used priorto delivering a shock to convert arrhythmias that are highlydisorganized. The use of fewer ATP therapy components reduces the numberof redetection periods that are enabled during the therapy delivery.

The diagram of FIG. 2 illustrates the concept of mapping associationsbetween morphological organization level and arrhythmia therapy inaccordance with embodiments of the invention. FIG. 2 depicts variousarrhythmia types, including for example, ventricular fibrillation (VF),polymorphic ventricular tachyarrhythmia (PVT), monomorphic ventriculartachyarrhythmia (MVT), and superventricular tachyarrhythmia (SVT). Eachof these arrhythmia types corresponds to one or more morphologicalorganization levels. In this example, the morphological organizationlevels are numbered 0-5 with 0 representing the most organizedarrhythmia, in this case, SVT, and 5 representing the most disorganizedarrhythmia, e.g., VF. More or fewer morphological organization levelsmay be used.

The use of additional organization levels provides therapy delivery thatis more finely tuned to the particular morphological organization levelof the arrhythmia. In some implementations, the arrhythmia morphologicalorganization level may be expressed as a continuous value. Therapyparameters, e.g., therapy times, therapy energies, therapy attempts, maybe adjusted based on the value of the morphological organization levelfor the particular arrhythmia.

Each morphological organization level is associated with a cardiactherapy, that may include multiple therapy components, e.g., ATP,cardioversion, or shock components. Parameters of the various cardiactherapies and/or therapy components are stored in memory in a therapylibrary (Rx library). In the particular example illustrated in FIG. 2,the cardiac therapy for each morphological organization level isdependent on the cardiac therapy of the previous level. In this example,each cardiac therapy adds a new therapy component as the morphologicalorganization level increases, e.g., level 1 is associated with ATP1,level 2 is associated with APT1→ATP2, level 3 is associated withATP1→ATP2→ATP3, and so forth. In other implementations, the cardiactherapy for each morphological level may be programmed to be independentof the cardiac therapy of the previous morphological organization level.For example, the cardiac therapy associated with level 4 may involveATP2→Cardioversion→Shock, and the cardiac therapy associated with level5 may only include the Shock components. The therapy components may beprogrammed to be delivered in any combination and/or in any order thateffectively treats the arrhythmia having the associated morphologicalorganization level.

In various implementations, the length of time that a therapy componentis attempted and/or the number of therapy components that are attemptedmay be programmed as a function of the morphological organization level.For each morphological organization level, the associated cardiactherapy may involve a sequence of therapy components queued in order ofaggressiveness or effectiveness. In such a scenario a “wander time” isassociated with each morphological organization level. Specifically,therapy to treat a less severe (more organized) arrhythmia may involve alonger wander time through the therapy library than the therapy to treata more severe (less organized) arrhythmia. For example, the longerwander time through the therapy library may result in more ATP therapycomponents delivered to convert the arrhythmia. As illustrated in FIG.2, therapy to treat a level 1 arrhythmia includes three ATP therapycomponents as compared to therapy to treat a level 3 arrhythmia whichincludes only one ATP therapy component.

Additionally, or alternatively, the length of time that a therapycomponent or a sequence of therapy components are attempted may be afunction of the morphological organization level. For example, if themorphological organization level is relatively low, corresponding to amore organized arrhythmia, then an ATP therapy component may bedelivered for a longer period of time before a shock is delivered ascompared to the period of time that an ATP therapy component isdelivered for a less organized arrhythmia. i.e., an arrhythmia having ahigher morphological organization level. A time out for one or asequence of ATP therapy components prior to delivering a more aggressiveor the most aggressive therapy may be longer from a more organizedarrhythmia than for a less organized arrhythmia. For example, one moreparameters of the cardiac therapy may be dependent on the morphologicalorganization level which may be expressed as a continuous variable. Forexample, the CRM device may be programmed to deliver the therapycomponent sequence ATP2→ATP3 for a period of time proportional to themorphological organization level. If the arrhythmia is not convertedafter the period of time, a more aggressive therapy is delivered, suchas a shock.

Parameters of the cardiac therapy and/or therapy components, and/ormapping between morphological organization levels and cardiac therapiesmay be static, meaning that for a particular patient, the cardiactherapy for each morphological organization level is time-invariantafter it is set, e.g., initially established in the device or set viathe device programmer. In one implementation, the therapy/therapycomponent parameters and associations between the morphologicalorganization levels and the cardiac therapies are made by the patient'sphysician communicating with a CRM device via a programmer. A userinterface program running on the programmer may step the physicianthrough a series of dialog boxes or prompts that allow the physician toset up the therapy/therapy component parameters and the organizationlevel to therapy mapping. In other implementations, the associations maybe initially mapped in the device to default values determined based atleast in part on clinical observations and may involve globaloptimization of clinical data. The default therapy parameters and/ormapping associations may take into account patient indications todevelop a more efficient therapy map. Once made and stored in the memoryof the device, the therapy associations may remain static until manuallychanged, e.g., changed by the physician.

In other embodiments, cardiac therapy parameters and/or mapping betweenmorphological organization levels and cardiac therapies may be dynamic.The therapy/therapy component parameters and/or organization level totherapy associations may be initially determined as in the static casepresented above and stored in the device memory. Following or duringtherapy delivery by the device to treat an arrhythmia episode, theefficacy of the therapy may be evaluated based on therapy efficacy. Thecardiac therapy parameters and/or mapping associations may be modifiedbased on the evaluation of therapy efficacy. For example, if the therapyis excessively aggressive for the particular morphological organizationlevel, the therapy parameters of the therapy components may be changed,or different, less aggressive, therapy components may be mapped to themorphological organization level. If the therapy is not sufficientlyaggressive to convert the arrhythmia in a timely fashion, the therapyparameters and/or the morphological organization level to therapymapping may be modified so that a more aggressive therapy is delivered.Various methods and systems for delivering adaptive tachyarrhythmiatherapy based on historical success, aspects of which may be utilized inthe embodiments presented herein, is described in commonly owned U.S.Pat. No. 6,801,806 which is incorporated herein by reference.

In some embodiments, the device may include circuitry for performingprocesses of dynamic modification for setting cardiac therapy parametersand/or mapping associations between morphological organization levelsand cardiac therapies. Dynamic modification of the cardiac therapyparameters and/or the mapping between organization levels and therapiesmay be performed during and/or after an arrhythmia episode. In somescenarios, the device may automatically change parameters and mappingduring therapy in an attempt to convert an occurring arrhythmia episode.In some scenarios, the modification of the therapy parameters and/ormapping may be retrospectively applied following conversion of anarrhythmia to a normal rhythm. For example, the device may evaluate theeffectiveness of the therapy sequence after the arrhythmia terminates todetermine if or how the therapy parameters and/or mapping would best bemodified.

The flowchart of FIG. 3 illustrates a process for dynamic modificationof the multi-level therapy described in connection with FIG. 2.Morphological organization levels may be initially associated withcardiac therapies based on physician input and/or default values aspreviously discussed. Initial cardiac therapy/therapy componentparameters, including therapy component sequences, time out intervals,wander time, burst rates, pace and/or shock energy levels, and/or otherparameters may be initially set.

If an arrhythmia episode is detected, the morphological organizationlevel of the arrhythmia is determined 320. Before or duringdetermination of the morphological organization level, the arrhythmiamay be classified as an arrhythmia that does not require treatment. Inthe example provided in FIG. 2, ventricular tachyarrhythmias are dividedinto five levels of morphological organization. Arrhythmias that areatrial in origin (SVTs) are classified as having a morphologicalorganization level of zero which is associated with no therapy delivery.The initial classification of an arrhythmia as VT or SVT may beperformed by any interval-based or morphology-based technique.

The morphological organization of the arrhythmia episode may be assessedusing a one or a combination of techniques. For example, morphologicalorganization may be assessed by analyzing the sensed cardiac electrogramsignal of the arrhythmia episode. Analysis of the electrogram signal mayinvolve determining the morphological regularity 322 of the electrogramsignal beats. In other implementations, the morphological organizationlevel may be assessed based on the entropy 324 associated with theelectrogram signal, or other measures of data distributions. Hemodynamicstability 326 is correlated to morphological stability of theelectrogram signal and may be used to determine the morphologicalorganization level. Other measures 328 of determining the morphologicalorganization level of the electrogram may alternatively or additionallybe used.

In some embodiments, a single one of the techniques described above maybe implemented to determine the morphological organization level of thearrhythmia episode. In other embodiments, a combination of techniquesmay be used. If a multiple techniques are used, then the morphologicalorganization level of the arrhythmia episode may be determined bycombining the results of the techniques by any data fusion method, suchas majority voting, or weighted average, for example.

Following determination of the morphological organization level, thefirst therapy component of the therapy scheme associated with theorganization level is delivered 330. A period of redetection may followdelivery of therapy component. If the arrhythmia is converted 350, thenthe therapy parameters and/or associations may be modified 370. If thearrhythmia is not converted 350, then additional therapy components ofthe therapy scheme are applied.

Modification of the therapy parameters and/or associations may be basedon the success or failure of the therapy to convert the arrhythmia. Forexample, if the therapy failed to convert the arrhythmia, then themorphological organization level/therapy association may be changed sothat the morphological organization level is associated with a moreaggressive therapy. On the other hand, if the therapy was highlysuccessful at converting the arrhythmia, e.g., if the arrhythmia wasconverted by the first component of the therapy, the morphologicalorganization level/therapy association may be remapped so that themorphological organization level is associated with a less aggressivetherapy. In the case of a highly successful therapy, remapping theorganization level/therapy association to provide a less aggressivetherapy may be attempted to increase device lifetime and enhance patientcomfort. In addition to modification of the morphological organizationlevel/therapy associations, one or more of the therapy parameters, e.g.,burst rate, stimulation energy, delivery time of one or more therapycomponents, and the like, may also be modified.

As discussed in connection with element 320 of FIG. 3, various processesmay be implemented to determine the morphological organization level ofthe arrhythmia episode. In one implementation, the morphologicalregularity 322 of the electrogram signal may be determined based on thenumber of similar beats in an arrhythmia episode. This implementation isillustrated by the flowchart of FIGS. 4A and 4B. The number of similarbeats in the arrhythmia episode is compared to thresholds associatedwith each morphological organization level.

FIG. 4A depicts a method for determining the number of similar beats inan arrhythmia episode. One or more features of a 1^(st) arrhythmiaepisode beat, denoted B1, are extracted 405. The extracted features ofB1 are used to form 410 a cardiac template. Cardiac templates mayinclude representative waveforms and/or information derived fromwaveforms, such as various attributes and/or ranges of attributes of thesensed cardiac signal, including, but not limited to: timing and/or rateinformation, QRS width, T-wave amplitude, Q-wave amplitude, QT interval,R-R intervals, interval statistics, or other intervals or attributesuseful for determining a correspondence between a cardiac waveform and atemplate. In this particular example, a cardiac waveform template isformed by identifying one or more cardiac waveform featuresrepresentative of a particular cardiac beat morphology. The particularwaveform features may include morphological features such as criticalpoints, significant points, curvature, local extrema, inflection points,rise or fall times, slopes, areas above and/or below baselines, andfrequency and/or wavelet coefficients, or the like.

A next beat, Bn, is detected and features extracted 415. The features ofBn are compared 420 to the template formed from the first beat todetermine the similarity of the Bn features to the template features.For example, the similarity of the beat to the template may be expressedin terms of a feature correlation coefficient (FCC). Methods and systemsfor determining similarity between episode beats and cardiac templatebeats based on calculating correlation coefficients are described incommonly owned U.S. Publication No. 2006/0074331 and incorporated hereinbe reference. Similarity between a beat and a template may be confirmed,for example, if the FCC is greater then a predetermined number, e.g.,about 0.9.

If the Bn is similar 425 to the template, then the counter for thetemplate is incremented 435. If Bn is not similar 425 to the template,T1, then another template is formed 450 based on the features of Bn. Theprocess continues as in blocks 415-455 by comparing additional episodebeats 445, 420 with previously formed templates 440 and forming 450 newtemplates if the beats are not similar to any of the previously formedtemplates. Each time a beat is similar to a template, the counter forthe template is incremented. If any beat matches an existing template,then the counter for that template is incremented 435. After all, asufficient number, or a representative sample of beats from thearrhythmia episode are evaluated 455, 456, the morphologicalorganization level may be determined 460 based on the counter valuesand/or the number of templates formed, for example.

FIG. 4B illustrates a process of determining the morphologicalorganization level based on the number of similar beats of an arrhythmiaepisode in accordance with embodiments of the invention. This processrelies on multiple thresholds, corresponding to a threshold measure ofsimilar beats for each morphological organization level. The thresholdsmay be expressed, for example, as a percentage of beats, or as apredetermined number of beats, e.g., x out of y beats, or as a number ofdistinct templates created, or in any other convenient form.

The highest counter value resulting from the process described inconnection with FIG. 4A represents the largest number of similar beatsin the arrhythmia episode. This value may be converted, for example, toa percentage or other measure. The measure of similar beats isdetermined 405 and is compared 410, 420, 430, 440 to a threshold foreach morphological organization level. If the measure of similar beatsis consistent with the threshold for a particular morphologicalorganization level, then the arrhythmia episode is classified 415, 425,435, 445, 455 as having that morphological organization level. Highlyorganized arrhythmias corresponding in this example to a morphologicalorganization level of 1, have the highest number or percentage ofsimilar beats. The most disorganized arrhythmias, corresponding in thisexample to morphological organization level 5, have the least number orpercentage of similar beats.

In another example, the morphological regularity of episode beats may bedetermined by calculating a spreadness of the beat features from atemplate. The morphological organization level may be determined basedon the spreadness of the beat features as illustrated in the flowchartof FIG. 5. The arrhythmia beats are detected and features of the beatsare extracted 505 for comparison to a template. In this example, eachbeat is compared 510 to the template by calculating a featurecorrelation coefficient (FCC), although other measures of similarity maybe used. The median FCC and the FCC spread are determined 515. Themedian FCC is the median value of the FCCs for all the beats of thearrhythmia episode used for morphological organization leveldetermination. The FCC spread is the number of FCC values that arewithin a window centered at the median FCC.

Morphological organization level is determined based on a FCC spreadthreshold associated with each organization level. The FCC spread iscompared 520, 530, 540, 550 to the threshold for each morphologicalorganization level. If the FCC spread is consistent with the thresholdfor a particular morphological organization level, then the arrhythmiaepisode is classified 525, 535, 545, 555, 565 as having thatmorphological organization level. Highly organized arrhythmiascorresponding in this example to a morphological organization level of1, have the highest FCC spread corresponding to the highest number ofFCC values within the window centered at the median FCC. The mostdisorganized arrhythmias, corresponding in this example to morphologicalorganization level 5, have the lowest FCC corresponding to the leastnumber of beats having FCC values within the window centered at themedian FCC. Methods and systems for determining morphological regularitysuch as those described herein are further discussed in commonly ownedU.S. Pat. No. 7,430,446, which is incorporated herein by reference.

In some embodiments, the morphological organization level of thearrhythmia may be based on determination of the complexity of thecardiac electrogram signal of the arrhythmia episode. The complexity ofthe electrogram may be quantified using sample entropy. Sample entropyis a statistical measure of the irregularity of complexity of a signalor system. A smaller sample entropy indicates a lower degree ofirregularity or a higher degree of complexity. A larger sample entropyindicates a higher degree of complexity Examples of using sample entropyin physiological signal analysis, are discussed in Lake et al., Am. J.Physiol. Regul. Integr. Comp. Physiol., 283: R789-97 (2002) and Richmanet al., Am. J. Physiol. Heart Circ. Physiol., 278: H2039-49 (2000).

Sample entropy may be computed for a signal recorded over a certainlength of time to indicate the degree of irregularity of the degree ofcomplexity of that signal. The signal is digitized into a sequence of nsamples: u(1), u(2), u(3), . . . u(n). In one embodiment, the sequenceis a sequence of scalars, i.e., each sample is a scalar. In anotherembodiment, the sequence is a sequence of vectors, i.e., each sampleu(i) is a vector of p scalars: u(i)=[u₁(i), u₂(i), u₃(i), . . .u_(p)(i)]. The following discussion of sample entropy applies when the nsamples are a set of scalars or a set of vectors.

The sequence of samples is divided into n−m+1 signal segments eachincluding m samples and denoted x_(m)(i)=[u(i), u(i+1), . . . u(i+m−1)],where 1≦i≦(n−m+1), and m is a number smaller than n and represents thelength of each signal segment. A vector matching score D_(m)(i,j)between x_(m)(j) and x_(m)(i), where j≠i, which is a measure ofsimilarity between the two signal segments, is given as follows:

$\begin{matrix}{{D_{m}( {i,j} )} = \{ \begin{matrix}{1,} & {{{L\lbrack {{x_{m}(j)},{x_{m}(i)}} \rbrack} \leq r};} \\{0,} & {{otherwise},}\end{matrix} } & (1)\end{matrix}$

where L is the maximum difference between corresponding components ofsignal segments x_(m)(j) and x_(m)(i) given by:

$\begin{matrix}{{L\lbrack {{x_{m}(j)},{x_{m}(i)}} \rbrack} = {\max\limits_{k = {0 \approx {m - 1}}}\{ {{L\lbrack {u( {{j + k},{u( {i + k} )}} \rbrack} \}},} }} & (2)\end{matrix}$

and r is a threshold. In one embodiment, the parameters n, m, and r areeach empirically determined. L indicates the similarity between signalsegments x_(m)(j) and x_(m)(i). In one embodiment, the sample entropy isgiven by:SampEn(m,n,r)=−ln [Γ(m,n,r)],  (3)

where:

$\begin{matrix}{{\Gamma( {m,n,r} )} = {\frac{\sum\limits_{i = 1}^{n - m - 1}{\sum\limits_{j = {i + 1}}^{n - m}{D_{m + 1}( {i,j} )}}}{\sum\limits_{i = 1}^{n - m - 1}{\sum\limits_{j = {i + 1}}^{n - m}{D_{m}( {i,j} )}}} \in {\lbrack {0,1} \rbrack.}}} & (4)\end{matrix}$

In one embodiment, SampEn is a parameter used to indicate the degree ofmorphological irregularity or complexity of the signal recorded over thecertain length of time. SampEn is compared to a plurality ofpredetermined entropy thresholds θ₁, θ₂, θ₃, . . . correspondingrespectively to morphological organization levels 1, 2, 3, . . . todetermine the morphological organization level of the arrhythmiaepisode. In another embodiment, Γ is a parameter used to indicate thedegree of morphological irregularity or complexity of the signalrecorded over time. Γ is compared to a plurality of predeterminedentropy thresholds γ₁, γ₂, γ₃, . . . corresponding respectively tomorphological organization levels 1, 2, 3, . . . to determine themorphological organization level of the arrhythmia episode.

In some implementations, the morphological organization level of thearrhythmia episode is determined based on using SampEn or Γ for analysisof the irregularity of the electrogram signal based on cycle length. Inother implementations, the morphological organization level of thearrhythmia episode is based on using SampEn or Γ for analysis of themorphological complexity of the electrogram. In further implementations,the morphological organization level of the arrhythmia episode isdetermined based on both analysis of the entropy associated with thecycle length irregularity of the electrogram signal and analysis of theentropy associated with the morphological complexity of the electrogramsignal. The use of entropy measures to analyze the morphologicalcomplexity of the electrogram signal by cycle length irregularitiesand/or morphological complexity is further described in commonly ownedU.S. Pat. No. 7,480,529, which is incorporated herein by reference.

In one embodiment, morphological organization can be estimated by usinghemodynamic sensor signals. Examples of these sensors include impedancesensors, pressure sensors, heart sound sensors, oxygen saturationsensors, activity sensors, and others. When hemodynamic sensors areused, the morphological organization determination may not necessarilybe based on the continuous recording of the sensor signal. Themorphological organization may be determined from parameters extractedfrom the signal morphology of the hemodynamic sensor signals which areable to characterize and quantify the hemodynamic compromise duringtachyarrhythmias. For example, if a pressure sensor is used, theparameters such as the mean value (computed over a designated period oftime), the variation of the pressure, the time derivative (dP/dt) of thepressure, and/or other features can be extracted or computed from thepressure sensor signal. Values of these features are then compared totheir respective thresholds, which may be determined during the normalsinus rhythm, to determine the morphological organization level of thearrhythmia.

In one embodiment, hemodynamic sensor signals may be used in conjunctionwith cardiac electrical signal sensors. When hemodynamic sensors areused together with the cardiac electrical activity sensors such as theelectrocardiography (ECG) or electrograms (EGM), the morphologyorganization can be first determined using the ECG or EGM only, usingthe methods such as the entropy or other morphology regularity measures.After the initial morphological organization is determined from the ECGor EGM, one or more hemodynamic sensor signals may be used to determinethe hemodynamic stability. Based on the stability determined using oneor more hemodynamic sensor signals, the initial morphologicalorganization level previously determined from the ECG/EGM only may beadjusted. Examples of the use of hemodynamic sensors in connection withdetection and treatment of cardiac arrhythmias are described in thefollowing U.S. patents which are incorporated herein by reference: U.S.Pat. No. 5,330,505 (describes the use of cardiac electrical sensorsand/or hemodynamic sensors used to adjust cardiac therapy) U.S. Pat. No.4,865,036 (describes the use of pre-ejection period as measured by anintracardiac impedance sensor to confirm tachyarrhythmia), U.S. Pat. No.5,176,137, (describes diagnosis of unstable tachyarrhythmia based inpart on oxygen saturation level), and U.S. Pat. No. 5,554,177,(describes the use of heart sound sensor to adjust cardiac therapy. Thetechniques of the incorporated by reference patents may be used inconjunction with the methods and systems for automatic multi-leveltherapy based on morphological organization of arrhythmia as exemplifiedby the embodiments of the invention presented herein.

Embodiments of the present system illustrated herein are generallydescribed as being implemented in a patient internal CRM device, whichmay operate to detect and deliver multi-level therapy for treatment oftachyarrhythmia. Various types of single and multiple chamber CRMdevices may be used to implement a number of pacing therapies as areknown in the art, in addition to delivering the tachyarrhythmia therapy.

It is understood that configurations, features, and combination offeatures described in the present disclosure can be implemented in awide range of implantable or external medical devices, and that suchembodiments and features are not limited to the particular devicesdescribed herein. The systems and methods described herein may beimplemented in a wide variety of implantable or external diagnosticand/or therapeutic cardiac devices such as defibrillators,cardioverters, pacemakers, cardiac monitors, and resynchronizers, forexample.

Although the present system is described in conjunction with animplantable cardiac defibrillator having a microprocessor-basedarchitecture, it will be understood that the implantable cardiacdefibrillator (or other device) may be implemented using any logic-basedintegrated circuit architecture, if desired.

In one embodiment, the CRM device is an implantablecardioverter/defibrillator configured as a single chamber device thatoperates to process cardiac signals and to deliver multi-level therapybased on morphological organization of the electrogram signals accordingto a methodology in accordance with the principles of the presentinvention. In another embodiment, the CRM device is an implantablecardioverter/defibrillator that is configured as a dual chamber device.In yet another embodiment, the CRM device is an implantablecardioverter/defibrillator configured to sense and/or provide electricalstimulation to multiple heart chambers, for example, both ventricles ofthe heart, as in a resynchronizer used to treat congestive heart failure(CHF).

Referring now to FIG. 6 of the drawings, there is shown one embodimentof a cardiac rhythm management system that may be used to implementtachyarrhythmia therapy selection methods of the present invention. Thecardiac rhythm management system in FIG. 6 includes a pulse generator(PG) 100 electrically and physically coupled to a lead system 110. Thehousing and/or header of the PG 100 may incorporate one or moreelectrodes 108, 109 used to provide electrical stimulation energy to theheart and to sense cardiac electrical activity. The PG 100 may utilizeall or a portion of the PG housing as a can electrode 109. The PG 100may include an indifferent electrode 198 positioned, for example, on theheader or the housing of the PG 100. If the PG 100 includes both a canelectrode 109 and an indifferent electrode 198, the electrodes 198, 109typically are electrically isolated from each other.

The lead system 110 is used to detect electric cardiac signals producedby the heart 190 and to provide electrical energy to the heart 190 undercertain predetermined conditions to treat cardiac arrhythmias. The leadsystem 110 may include one or more electrodes used for pacing, sensing,and/or cardioversion/defibrillation. In the embodiment shown in FIG. 6,the lead system 110 includes an intracardiac right ventricular (RV) leadsystem 104, an intracardiac right atrial (RA) lead system 105, anintracardiac left ventricular (LV) lead system 106, and an extracardiacleft atrial (LA) lead system 108. The lead system 110 of FIG. 6illustrates one embodiment that may be used in connection with the multilevel tachyarrhythmia therapy methodologies described herein. Otherleads and/or electrodes may additionally or alternatively be used.

The lead system 110 may include intracardiac leads 104, 105, 106implanted in a human body with portions of the intracardiac leads 104,105, 106 inserted into a heart 190. The intracardiac leads 104, 105, 106include various electrodes positionable within the heart for sensingelectrical activity of the heart and for delivering electricalstimulation energy to the heart, for example, pacing pulses and/ordefibrillation shocks to treat various arrhythmias of the heart.

As illustrated in FIG. 6, the lead system 110 may include one or moreextracardiac leads 108 having electrodes, e.g., epicardial electrodes,positioned at locations outside the heart for sensing and/or pacing oneor more heart chambers.

The right ventricular lead system 104 illustrated in FIG. 6 includes anSVC-coil 116, an RV-coil 114, an RV-ring electrode 111, and an RV-tipelectrode 112. The right ventricular lead system 104 extends through theright atrium 120 and into the right ventricle 119. In particular, theRV-tip electrode 112, RV-ring electrode 111, and RV-coil electrode 114are positioned at appropriate locations within the right ventricle forsensing and delivering electrical stimulation pulses to the heart. TheSVC-coil 116 is positioned at an appropriate location within the rightatrium chamber of the heart 190 or a major vein leading to the rightatrial chamber of the heart 190.

In one configuration, the RV-tip electrode 112 referenced to the canelectrode 109 may be used to implement unipolar pacing and/or sensing inthe right ventricle. Bipolar pacing and/or sensing in the rightventricle may be implemented using the RV-tip 112 and RV-ring 111electrodes. The RV-ring 111 electrode may optionally be omitted, andbipolar pacing and/or sensing may be accomplished using the RV-tipelectrode 112 and the RV-coil 114, for example. Sensing in the RV mayinvolve the tip-to-ring vector and the RV-coil to SVC-coil or theRV-coil to SVC coil electrically tied to the can vector. The rightventricular lead system 104 may be configured as an integrated bipolarpace/shock lead. The RV-coil 114 and the SVC-coil 116 are defibrillationelectrodes.

The left ventricular lead 106 includes an LV distal electrode 113 and anLV proximal electrode 117 located at appropriate locations in or aboutthe left ventricle for pacing and/or sensing the left ventricle. Theleft ventricular lead 106 may be guided into the right atrium of theheart via the superior vena cava. From the right atrium, the leftventricular lead 106 may be deployed into the coronary sinus ostium, theopening of the coronary sinus. The lead 106 may be guided through thecoronary sinus to a coronary vein 124 of the left ventricle. This veinis used as an access pathway for leads to reach the surfaces of the leftventricle that are not directly accessible from the right side of theheart. Lead placement for the left ventricular lead 106 may be achievedvia subclavian vein access and a preformed guiding catheter forinsertion of the LV electrodes 113, 117 adjacent to the left ventricle.

Unipolar pacing and/or sensing in the left ventricle may be implemented,for example, using the LV distal electrode 113 referenced to the canelectrode 109. The LV distal electrode 113 and the LV proximal electrode117 may be used together as bipolar sense and/or pace electrodes for theleft ventricle. The left ventricular lead 106 and the right ventricularlead 104, in conjunction with the PG 100, may be used to provide cardiacresynchronization therapy such that the ventricles of the heart arepaced substantially simultaneously, or in phased sequence, to provideenhanced cardiac pumping efficiency for patients suffering from chronicheart failure.

The right atrial lead 105 includes a RA-tip electrode 156 and an RA-ringelectrode 154 positioned at appropriate locations in the right atriumfor sensing and pacing the right atrium. In one configuration, theRA-tip 156 referenced to the can electrode 109, for example, may be usedto provide unipolar pacing and/or sensing in the right atrium 120. Inanother configuration, the RA-tip electrode 156 and the RA-ringelectrode 154 may be used to effect bipolar pacing and/or sensing.

FIG. 6 illustrates one embodiment of a left atrial lead system 108. Inthis example, the left atrial lead 108 is implemented as an extracardiaclead with an LA distal electrode 118 positioned at an appropriatelocation outside the heart 190 for sensing and pacing the left atrium.Unipolar pacing and/or sensing of the left atrium may be accomplished,for example, using the LA distal electrode 118 to the can 109 pacingvector. The left atrial lead 108 may be provided with additionalelectrodes used to implement bipolar pacing and/or sensing of the leftatrium.

Referring now to FIG. 7, there is shown a block diagram of an embodimentof a CRM device 200 employing a PG 260 suitable for implementingmulti-level tachyarrhythmia therapy methodologies of the presentinvention. FIG. 7 shows the CRM device 200 divided into functionalblocks. There exist many possible configurations in which thesefunctional blocks can be arranged. The example depicted in FIG. 7 is onepossible functional arrangement. The CRM device 200 includes circuitryfor receiving cardiac signals from a heart and delivering electricalenergy in the form of pace pulses or cardioversion/defibrillation pulsesto the heart.

A cardiac lead system 210 may be implanted so that cardiac electrodesare electrically coupled to the heart tissue as described above inconnection with FIG. 6. The cardiac electrodes of the lead system 210sense cardiac signals associated with electrical activity of the heart.The sensed cardiac signals may be transmitted to a PG 260 through thelead system 210. The cardiac electrodes and lead system 210 may be usedto deliver electrical stimulation generated by the PG 260 to the heartto mitigate various cardiac arrhythmias. The PG 260, in combination withthe cardiac electrodes and lead system 210, may detect cardiac signalsand deliver therapeutic electrical stimulation to any of the left andright ventricles and left and right atria, for example. For example, thePG 260 may deliver ATP, cardioversion, and/or defibrillation shocks tothe heart through the lead system 210 in accordance with a multi-leveltachyarrhythmia therapy of the present invention. A can electrode 205coupled to a housing of the PG 260 may additionally be used to sensecardiac signals and deliver electrical stimulation to the heart.

In one embodiment, PG circuitry 201 is encased in a hermetically sealedhousing suitable for implanting in a human body. Power is supplied by anelectrochemical battery 230 that is housed within the PG 260. In oneembodiment, the PG circuitry 201 is a programmable microprocessor-basedsystem, including a control system 250, EGM sensing circuit 220 and atachyarrhythmia therapy circuit 215, which may include pacing and shocktherapy components. The PG circuitry 201 may also include a memory 240.The memory 240 may be used to store a therapy library 241 that includesassociations between morphological organization level of a cardiacsignal of a type of arrhythmia and therapies to treat arrhythmias. Thememory 240 may be used to store parameters of the therapy and therapycomponents, and other parameters and/or data. The parameters and datastored in the memory 240 may be used on-board for various purposesand/or transmitted via telemetry to an external programmer unit 245 orother patient-external device, as desired.

In one embodiment, the PG circuitry 201 includes drive/sense circuitry221 for the operation of one or more hemodynamic sensors 211. Thesignals produced by the sensor circuitry 211, 221 may be used todetermine morphological organization level of the arrhythmia aspreviously described.

The control system 250 may used to control various subsystems of the PG260, including the tachyarrhythmia therapy circuit 215, the electrogramsensing circuitry 220. The control system 250 may also include templatecircuitry for providing or processing one or more templates used indetermination of the morphological organization of the electrogramaccording to embodiments of the invention.

Communications circuitry 235 allows the PG 260 to communicate with anexternal programmer unit 245 and/or other patient-external system(s). Inone embodiment, the communications circuitry 235 and the programmer unit245 use a wire loop antenna and a radio frequency telemetric link toreceive and transmit signals and data between the programmer 245 andcommunications circuitry 235. In this manner, programming commands maybe transferred to the PG 260 from the programmer 245 during and afterimplant. In addition, stored cardiac data may be transferred to theprogrammer unit 245 from the PG 260, for example.

Sensing circuitry 220 detects cardiac signals sensed at the cardiacelectrodes 210. The sensing circuitry may include, for example,amplifiers, filters, ND converters and other signal processingcircuitry. Cardiac signals processed by the sensing circuitry may becommunicated the control system 250, to the arrhythmia detector 254, andto the morphological organization processor (MOP) 256.

The arrhythmia detector 254 detects the presence of an arrhythmia, forexample, by evaluating the rate and/or morphology of the electrogramsignal. The MOP 256 performs various processes associated withdetermination of the morphological organization level of an arrhythmiaepisode. For example, the MOP 256 may use perform processes identifiedin the flowcharts of FIGS. 3, 4A, 4B, and 5. The MOP 256 may includeimplementations in hardware, software, and/or firmware.

The MOP 256 analyzes the signals from the electrogram sensing circuitryand/or the sensor circuitry to determine the morphological organizationlevel of the detected arrhythmia episode. For example, the MOP 256 mayevaluate the cardiac electrogram signal to determine the morphologicalregularity of the signal. The MOP 256 may alternatively or additionallyanalyze the cardiac electrogram signal to determine the entropy, e.g.,irregularity and/or complexity, of the signal. Further, the MOP 256 mayalternatively or additionally analyze signals derived from one or morehemodynamic sensors 211 to determine the hemodynamic stability of thearrhythmia episode. The MOP 256 determines the morphologicalorganization level of the arrhythmia based on analysis of theelectrogram and/or sensor signals.

Based on the morphological organization level of the arrhythmia episode,the MOP 256 accesses the therapy library 241 to identify a therapyassociated with the morphological organization level of the arrhythmia.The tachyarrhythmia therapy circuit 215 controls delivery of theidentified therapy. The MOP 256 may initialize and/or modify the therapyparameters and/or mapping associations between the morphologicalorganization levels and therapies. For example, the MOP 256 may modifythe morphological organization level to therapy associations and/ortherapy parameters based on the success or failure of the deliveredtherapy as previously described. The new parameters and/or associationsare stored in the therapy library 241.

Various modifications and additions can be made to the preferredembodiments discussed hereinabove without departing from the scope ofthe present invention. Accordingly, the scope of the present inventionshould not be limited by the particular embodiments described above, butshould be defined only by the claims set forth below and equivalentsthereof.

What is claimed is:
 1. A cardiac rhythm management device, comprising: aprocessor configured to associate morphological organization levels ofarrhythmias with cardiac therapies, the morphological organizationlevels related to cardiac signal morphologies of the arrhythmias; ahemodynamics sensor, wherein the processor is configured to determine amorphological organization level of an arrhythmia episode based on anoutput of the hemodynamics sensor and a measure of a morphologicalorganization reaching a threshold; an arrhythmia detector configured todetect the arrhythmia episode and redetect subsequent arrhythmiaepisodes, wherein a frequency of the redetection is based on a degree oforganization of the morphological organization level; and a therapycircuitry configured to deliver a cardiac therapy associated with themorphological organization level of the arrhythmia episode.
 2. Thedevice of claim 1, wherein the processor is configured to determine themorphological organization level of the arrhythmia episode based, on atleast one of morphological regularity of a cardiac electrogram signal ofthe arrhythmia episode, entropy of the cardiac electrogram signal, rateregularity of the arrhythmia episode, and hemodynamics of the arrhythmiaepisode.
 3. The device of claim 1, wherein the processor is configuredto compare morphologies of one or more cardiac beat signals of thearrhythmia episode to a template to determine the morphologicalorganization of the arrhythmia episode.
 4. The device of claim 1,wherein the processor is configured to compare a morphology of onecardiac beat signal of the arrhythmia episode to a morphology of anothercardiac beat signal of the arrhythmia episode to determine themorphological organization of the arrhythmia episode.
 5. The device ofclaim 1, wherein the hemodynamics sensor comprises an impedance sensor.6. The device of claim 1, wherein the hemodynamics sensor comprises apressure sensor.
 7. The device of claim 1, wherein the processor isconfigured to associate the morphological organization levels with thecardiac therapies based on one or more of retrospective databaseanalysis, patient therapy tolerance, and physician input.
 8. The deviceof claim 1, wherein the therapy circuitry is configured to deliver oneor more of an anti-tachyarrhythmia pacing therapy and a shock therapy.9. The device of claim 1, wherein the redetection occurs with morefrequency based on a more organized arrhythmia episode and with lessfrequency based on a less organized arrhythmia episode.
 10. The deviceof claim 1, wherein the processor is configured to statically associatethe morphological organization levels with the cardiac therapies. 11.The device of claim 1, wherein the processor is configured todynamically associate the morphological organization levels with thecardiac therapies.
 12. The device of claim 1, wherein the processor isconfigured to modify the association of the morphological organizationlevels with the cardiac therapies based on efficacy of the cardiactherapies.
 13. The device of claim 1, wherein the processor isconfigured to determine an efficacy of the delivered cardiac therapy andto modify at least one of the morphological organization levelassociated with the cardiac therapy and a therapy parameter based on theefficacy of the delivered cardiac therapy.
 14. The device of claim 1,further comprising a memory, wherein the memory stores a library of thecardiac therapies and an association map between the morphologicalorganization levels and the cardiac therapies.
 15. The device of claim1, wherein the device is patient implantable.